Although the invention is not limited thereto, it will be exlained hereinafter for a use in which it has particular utility. Such use is determining a position of a member in a fluid pressure activated work cylinder.
Prior to the present invention, it has been known in the prior art to use potentiometers in this application. See, for example, German publication DE 35 20 199A1. The potentiometer taught in this publication includes a resistance track and a contact member. The contact member is moved and guided along the resistance track by means of an activating member. The resistance track and contact member are generally positioned within a housing in order to provide protection of such contact member and the resistance track against dust and humidity which can damage the components. The activating member generally consists of a rod-like-shaped body. This rod-shaped activating member projects through an opening which is provided in the housing. A sealing means is provided to seal the rod-shaped activating member at the opening of the housing.
When the potentiometer described above is used for indicating the relative position of a piston in a work cylinder, it is necessary to arrange the resistance track mounting so that it can be rigidly attached to the housing of the work cylinder and to connect the activating member with either the piston or with the piston rod of such work cylinder.
For the purpose of operational integrity, it is an advantage to provide an arrangement of the contact member in such a way that it is relatively secured against an undesirable rotation on a theoretical axis which is in the direction of the movement of the contact member along the resistance track.
Furthermore, in order to enable rotation of the piston rod about its longitudinal axis in relation to the work cylinder, it has been taught, in the above-referenced German publication, that a joint is necessary. This joint is located between the activating member and the contact member. This arrangement on the joint constitutes a greater utilization of components which will be subjected to wear. In addition, this arrangement results in a relatively high level of manufacturing tolerances which add to the equipment costs as well as to the maintenance costs.